Background: In the past decade, advances in upper limb socket design and technology have been proposed to increase comfort and decrease perceived weight of the prosthesis. The VA Study to Optimize the DEKA Arm employs one such design, the high fidelity socket interface, to increase comfort, stability, and tolerance of the weight of the DEKA prosthesis. However, no research studies have been conducted to validate these claims or compare this socket design to a more traditional design. Objectives: The purpose of this pilot study is to conduct a head to head comparison of two candidate socket designs: the traditional TH socket design and the high fidelity socket design. The specific objectives are to: 1) optimize the XROMM system for the measurement of skeletal kinematics while wearing a transhumeral prosthetic socket, 2) compare comfort, perceived stability, perceived prosthetic weight, and ease of donning and doffing of two upper limb socket designs, and 3) determine bone, joint and sockets kinematics during active range of motion (ROM), vertical loading, and resisted activities. Methods: A cadaver study will be conducted to examine static and dynamic accuracy of the XROMM system, and to refine the motion tracking and analysis algorithms prior to use in the human subjects portion of the study. Two subjects with transhumeral amputation will be randomly assigned to one of two groups traditional socket, first group or high fidelity socket first grop. Each subject will be fit with the appropriate prosthetic socket and will wear that socket for two weeks of home use. Following home usage of the first socket, the subject will return to the VA to be surveyed about comfort, stability, perceived weight of their prosthesis, and ease of donning and doffing. The process will be repeated with the second socket design. Survey results will be compared qualitatively. XROMM as well as conventional optical motion capture will be used to study the motion of the socket with respect to the distal residual humerus. XROMM data will be generated during active shoulder range of motion, high demand vertical loading, and resisted activities. We will also characterize soft tissue motion artifacts associated with measuring upper extremity motion with skin marker-based optical motion tracking systems. Using these techniques, we will examine: motion of residual bone within the socket, axial rotation of soft tissue around the limb, axial rotation of socket around the limb, slip of the socket during vertica loading, and translation of socket: any gross movement (excluding axial rotation) of the interface around the limb. Significance: The high fidelity upper limb socket design has been advocated to improve comfort, increase socket stability and improve suspension during weighted activities. However, no research studies have been conducted to validate these claims or compare this socket design to a more traditional design. This pilot study will use subject surveys, functional testing and advanced kinematic analysis to compare high fidelity and traditional socket designs. Our study will employ cutting edge methodology of bi-plane videoradiography (XROMM), as well as evaluate the capabilities and limitations of traditional optical motion capture methods using the XROMM as the gold standard for dynamic skeletal motion measurement. Although preliminary studies have been conducted to examine the interface of lower limb prosthetics. Bi-plane videoradiography has not been applied to analysis of the upper extremity prosthetic fit. This pilot study will provide preliminary data to guide decisions regarding upper limb prosthetic socket prescription for future VA studies of advanced upper limb prosthetics.